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Case Study: Municipal Wastewater Treatment -Sludge Dewatering


A 5.7 MGD treatment works in Spain is located in a holiday and resort area.

  • Blended primary/secondary biosolids are thickened and dewatered using centrifuges at a flowrate of 26 gpm, 10 hours/day.
  • The dewatering room is vented to a bio-filter scrubber.


The biosolids are septic resulting in high hydrogen sulfide emissions and dangerous working conditions.

  • The plant experiences a fatality due to 70-150 ppm H2S emissions in the dewatering room. Operators suffer from eye irritation/temporary blindness.
  • Nuisance odor complaints due to primary clarifier and bio-filter emissions.


976 - UNITED CAIROX® Potassium Permanganate is injected into the raw sludge pipeline, prior to the centrifuges.
A full-scale plant demonstration determined the optimum dosage to be 10 lb potassium permanganate/hour (800 mg/L)


CAIROX treatment lowered the H2S from 70-150 ppm to non-detectable in the dewatering room.
Bio-filter exhaust drops from 20 ppm to ND.